How to get into Atari hardware repair?

[Trip3nite]

Hey there
A few days ago I tried to install an exxos 4mb upgrade in my 1040ST, which isn't working so far.
Either I made a soldering mistake somewhere and killed my upgrade board, my MMU is not making contact, or my board for some reason can't power both my stock ram and the upgrade at the same time.
I would love that I could just find out where the fault lies when something like this happens, but I don't know much about this stuff.
I'm ok at soldering cause I've done some kits for some retro gaming stuff and repairs to my guitars before, but no clue about these, I was just following guides anyway.
Also, someone once gave me 2 1040ST's with broken boards, as he was gonna throw those out otherwise, but I have no idea what the problem is (those got me wanting to buy a functioning one in the first place), and someone else I know said that if I was gonna get into this, he also has a broken 520ST and 2 broken 1040ST's he wanted to give me.
Would love to be able to get those up and running as well, so I can have one set up for gaming, one for music, and some spare machines to either keep or sell, or keep for parts if they're beyond repair, or maybe use one for parts to try making that H5 board too.
I have been watching a lot of Adrians Digital Basement video's of him repairing old computers, he's reviewed some cheap scopes which seem to do the trick for these old machines, and the troubleshooting he does is often pretty straightforward, usually just following a bad signal to its source and replacing the part or fixing the trace where things seem to be going wrong.
It's not like this stuff looks simple to me, but it also doesn't look like rocket science which seems too daunting for me to tackle, so I'd love to get into it.
Any advice or good starting points to learn about this stuff?

[exxos]

It's a tricky one. Because it's not the computer you need to start with. It's leaning general basic electronics and fault finding skills. For me, I have always been interested in electronics and computers. I took a 2 year intensive electronics training course and then did a year work placement in a workshop that repaired all sorts of electronics equipment. Real world practical experience is invaluable.

It's actually a interesting problem overall. Since there are basically zero guides and channels dedicated to Atari repair. It's why I document all my work and findings all the time so people can learn from it all. It's why the fixes forum exists.

I'd suggest you start by looking at our basic troubleshooting forum which is likely the only source of information at the moment. Of course the problem becomes, we can't really teach basic electronics. You really need to take some courses for that.

viewforum.php?f=91

I did write a basic H4 checking guide a while back. It's still valid for original machines for the best part.

viewtopic.php?f=78&t=2362

Another huge problem is machines can have multiple things wrong with them. If the machine doesn't display a picture. It could be the power supply. It might not be, it could be a bad reset switch.. bad ram. Bad MFP solder joint. I've had to resolder half the motherboard by now to get it working. So you have to be methodical in working though each likely failure point. Most of the time you have to guess and just try stuff.

For example, if the soldering looks iffy on the MMU or whatever. Rather than trying to figure out bad connections, it's just quicker to resolder it. However, if your not good at soldering, you could actually make things worse as a lot of people seem to do. Endless trial and error and being to stubborn to quit is a must.

This is why you need multiple machines. You need test machines for various use cases. I've got about 30 test machines for testing all sorts. If a RAM upgrade doesn't work and others stop working, I can try it in another machine to rule out some stuff. In your case, you don't know if the RAM upgrade is working. You need a second or even 3rd machine.

Dave Jones EEVblog has thousands of electronics videos to learn about all sorts.

[rubber_jonnie]

What @exxos says is all very valuable information, and the key thing is that it takes time, there are no shortcuts.

Can I fix old computers? Sure, I've revived ZX81's, Spectrums, 16 & 8 bit Ataris, TRS-80's and many more. Can I design stuff? Nothing beyond basic circuits.

For my own personal journey, it's probably only in the last 5 or 6 years that I have got any good at fault diagnosis and repairs, purely and simply because I chose to learn. You may notice that I started the Basic Troubleshooting section, and with the help of the people here on this forum it's slowly improved.

Luckily I had a basic understanding of electronic components and their functions, including logic gates etc, and you'll need that really to start to understand what you see on schematic diagrams, as they are key to figuring stuff out.

So yes, as well as understanding components, you'll need to know how to read schematics and datasheets too.

I am still learning all the time, take my Spectrum thread, it took help from the great people here to understand what the 12v circuit was and how it worked, but once I did I was able to get to the root of the problem, and also highlighting the need to double check things like transistor pinouts.

So do your reading, take your time, and don't dive in unless you have some sort of plan. If you planning on learning to solder, don't do it on STs, buy cheap kits and make your mistakes where it won't brick something precious, and watch some videos that highlight the problems you can run into, such as large ground or power planes that suck heat away, and how easy it can be to lift traces.

[Trip3nite]

Thanks for the tips!
I'll definitely check out those forum topics and videos!

Today I actually got one of those other 2 boards running too! I have to admit I was just lucky it was so simple though.
I just connected a monitor and turned them on, one of them didn't do anything, the other one did but the output was all glitchy. (random amounts of bombs too)
Looked at the under side of the board and saw there had been some soldering work done to the shifter socket, or a socket was installed.
I cleaned it and wouldn't have even noticed there was work done if there wasnt a bunch of flux, but I checked the connections of the socket for shorts and continuity anyway, and all seemed good.
I cleaned and reseated the shifter which didn't do anything, so then I thought I could try the shifter from that other dead board, so I popped it in and it seems to be working now!
Don't have any diagnostics cartridge, but it does boot into tos and I kept it running for 15 min without glitching or bombs appearing.
So I think I actually have 2 working boards now.
I just tried the 4mb upgrade on that board and I get the same problem as on the other board (black screen and a continuous beep coming from the monitor, which is monochrome btw, problem goes away when put back to stock)
Still don't have a thing to pull the MMU chip and clean it before trying the upgrade again, but I guess the more logical thing is that my upgrade board is dead, as I get exactly the same symptoms in both systems, but either way I'm gonna get a tool to pull the mmu chip and clean it so I can rule that out.
I did buy this 4mb upgrade kit years ago when I first received those dead machines, and never got to installing it as i didn't find someone who would fix it for less money than buying a new one, so it has been just sitting somewhere in the basement for years, but I guess I just probably broke it myself.
I still don't find anything wrong with the shifter board, even checked continuity from the socket to the ends of the ribbon connector according to the schematic, and everything is connected as it should be.
Could i have maybe damaged the 4mb upgrade by not having seated the shifter board/chip or mmu board correctly?
I put them in with the right orientation but maybe didn't make all connections....
I think it must be either that, or I happen to have 2 boards that can't handle 2 sets of ram getting powered, they are the same revision though, so maybe.
If cleaning the MMU doesnt work, I'm thinking of just removing the ram by clipping the chips and desoldering pins according to Adrians Digital basements suggestion, as I have no desoldering gun and no experience with those anyway...
If that also doesn't work, I think I just have a broken upgrade...

Anyway, was going a bit off topic, but I really liked seeing my desktop open on that other machine today, even though it was just some trial and error... Pretty determined on at least trying to get that third one running too now, and get the 4mb upgrade working too.
I'm definitely gonna check some more vids on basic electronics.
If this stuff keeps interesting me so much, I'm thinking to maybe also get one of those vic20 or C64 replica boards to try and populate to get a feel of how these things work, always wanted one of those anyway, as I always heard my stepdad talking about how he first started programming on those.
I go through these phases of being super interested in random things so idk whether this will last, but either way I just want to get and keep these machines running for games and music production.
I know these computers often fail after almost 40y now, and I just don't want to have to send them off to some specialist guy to pay them more to fix my machines than I would pay to buy another one.

[rubber_jonnie]

With the MMU adapter, the best advice I can give is to make sure the machine is out of the board when you fit it, and on a flat surface, I'd suggest on a piece of cardboard, which will give a little, but still be firm enough to press down without the board bending.

Be 100% sure that pin one of the adapter is correctly aligned with pin 1 of the MMU, as some boards changed the MMU orientation, and once it's pressed in, you should have a gap of no more than about 2mm between the top of the MMU and the bottom of the adapter.

Also be sure the ribbon cable between the MMU and Shifter adapter is the right way up, or you won't get a connection.

Last thing, be 100% sure the onboard RAM is 100% disabled as described in the fitting instructions, 4MB is the max for any ST, so if any is left connected, i.e. not disabled, you're going to have problems.

[Trip3nite]

With the MMU adapter, the best advice I can give is to make sure the machine is out of the board when you fit it, and on a flat surface, I'd suggest on a piece of cardboard, which will give a little, but still be firm enough to press down without the board bending.

Be 100% sure that pin one of the adapter is correctly aligned with pin 1 of the MMU, as some boards changed the MMU orientation, and once it's pressed in, you should have a gap of no more than about 2mm between the top of the MMU and the bottom of the adapter.

Also be sure the ribbon cable between the MMU and Shifter adapter is the right way up, or you won't get a connection.

Last thing, be 100% sure the onboard RAM is 100% disabled as described in the fitting instructions, 4MB is the max for any ST, so if any is left connected, i.e. not disabled, you're going to have problems.

I did all things you said here, and the mmu adapter indeed sits just about 2mm above the MMU
This made me think of something though...
As per the instructions of the kit for a silly style revision, I shortened the pins of the mmu board, so maybe it could fit in even deeper?
It does look about the same as in the pictures in the guide though, and i already had to press down pretty hard to get it as deep as it is right now.
Would have taken a pic but both of them are back to stock atm... Could do it tomorrow though

[exxos]

As per the instructions of the kit for a silly style revision, I shortened the pins of the mmu board, so maybe it could fit in even deeper?

Now knowing this, did you try the board before cutting the pins ? If you cut them to short or not totally level then they may not make contact in the socket anymore.

Probably a good step is to scope the circled pins on the MMU board as those are the "active" signals. Though you have to really do this on power up as the MMU likely would disable "bad" banks of RAM. So the signals wouldn't switch for very long.

[Trip3nite]

As per the instructions of the kit for a silly style revision, I shortened the pins of the mmu board, so maybe it could fit in even deeper?

Now knowing this, did you try the board before cutting the pins ? If you cut them to short or not totally level then they may not make contact in the socket anymore.

Actually I assumed I did when i received it years ago, don't remember too well but i originally bought it for that other board which is also a silly style board, also soldered the new psu cables back then, but never got further than that as my atari board was still broken.
It definitely looks shorter than the pins in the guide so I think i did, but they looked really uniform in length so not 100% sure, I'll post a picture tomorrow!

[Trip3nite]

I figured I could already post a pic of the board, just not gonna start tinkering with stuff again today.
Do these boards come with pins that size? They definitely look smaller than the one in the picture from the guide in the background.

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[exxos]

They look like the normal pins.

So I think you missed the info for that image..

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